1) Field of the Invention
The present invention relates generally to agricultural sprayers and, more specifically, to suspension and steering systems for such sprayers.
2) Related Art
Self-propelled crop sprayers such as the John Deere Model 6500 Sprayer are often required to operate over rough ground surfaces and in tall mature crops. Various devices are used to help cushion the vehicle and operator from the effects of rough surfaces, but most suffer from one or more disadvantages such as limited cushioning or bulkiness leading to increased interference with the crop being sprayed. A cushioned wheel arrangement, such as the front wheel suspension shown in U.S. Pat. No. 5,066,030, is available for relatively small sprayers with a single steerable wheel. However, such a suspension is not suitable for most larger sprayers or sprayers having two or more steerable wheels. Some available self-propelled sprayers have strut suspensions on the front axle, but lack a cushioned suspension or have an arm-type of suspension on the rear.
Steering arrangements for sprayer wheel assemblies that are cushioned include those with steering arms at the tops the strut shafts. Such top mounted arm arrangements suffer from the problem of undesired movement of the steerable wheels over rough ground surfaces, referred to as bump steering, as the steering arms move up and down with the strut shafts.
Often, sprayer suspensions include strut shafts with steel suspension springs immersed in oil, but these are subject to leakage, and enclosing the springs requires relatively large diameter supports both above and below the axle. Providing adequate cushioning over a substantial range of vertical wheel movement without adversely affecting crop clearance continues to be a problem.
The row spacings in row crop situations can vary from field to field so that the wheel tread of the spray vehicle has to be adjusted accordingly. An adjustable axle for a sprayer is shown in copending and commonly assigned U.S. application Ser. No. 08/372,751 entitled "Adjustable Axle with Shim Structure" filed 13 Jan. 1995, now U.S. Pat. No. 4,071,277. Machines with transversely adjustable steerable wheels usually must have some kind of adjustable steering linkage to accommodate wheel tread adjustment. Making the necessary linkage adjustments when wheel tread is changed can be time-consuming and inconvenient. Providing good visibility from the cab of the sprayer and maintaining a direct line of sight from the cab to the wheels of the sprayer have often been a problem also.